JPS63191B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a torque control device that controls the tightening torque of an electric screwdriver driven by a DC motor in two stages.

Conventionally, electric drivers driven by a DC motor with a characteristic that the load current is proportional to the tightening torque detect the load current flowing through the DC motor in order to control the tightening torque, and detect the load current when it reaches a predetermined value. When this occurs, the voltage supplied to the DC motor is cut off to control the tightening torque. In this type of electric screwdriver, when the screw head seat comes into contact with the mating material and the load current reaches a value corresponding to the desired tightening torque, the DC motor tries to stop rotating, but the screwdriver bit stops rotating due to inertia. Rotate further. This rotational torque becomes tightening torque and is applied to the screw, and the tightening torque applied to the screw reaches more than the tightening torque specified by the load current of the DC motor, which has the disadvantage that torque control cannot be performed accurately. It is occurring.

The present invention aims to eliminate the above-mentioned drawbacks.
Examples will be described below with reference to the drawings. In FIG. 1, 1 is a switching circuit, 2 is a first voltage setting circuit, and 3 is a switching circuit.
is a final voltage setting circuit, and the switching circuit 1 connects the first voltage setting circuit 2 as a voltage supply section to the setting 6 by a screw tightening start signal, and connects it to the DC motor 6 by an output signal from a comparison circuit 9 to be described later. The voltage supply unit to be supplied is switched from the first voltage setting circuit 2 to the final voltage setting circuit 3. This first voltage or final voltage is transmitted to the drive circuit through an amplifier circuit, and the final voltage is configured to pass through a delay circuit 11 consisting of a capacitor and a resistor so as to gradually increase. The first voltage and the final voltage are respectively applied to the DC motor 6 when no load is applied.
This specifies the rotational speed of the DC motor 6 and the maximum rotational torque that the DC motor 6 has.As the load applied to the DC motor 6 increases, the rotation of the DC motor 6 decreases until the DC motor 6 stops. When the DC motor 6 is in a saturated state, the DC motor 6 is configured to output the maximum rotational torque. In addition, the first voltage is applied to the DC motor 6 to perform the screw tightening work by appropriately supplying the voltage to the DC motor 6 before starting the full-scale work,
The actual tightening torque applied during screw tightening is measured using a torque wrench, and the operator repeatedly makes adjustments so that the measured value does not reach the desired tightening torque. In this adjustment stage, the actual tightening torque is influenced by the inertia of the rotating part of the DC motor, and the inertia also changes depending on the rotation speed of the rotating part, so the actual tightening torque should be appropriately smaller than the desired tightening torque. It is necessary to keep it. The final voltage is determined by applying a voltage higher than the first voltage to the DC motor from a circuit separate from the first voltage, rotating the DC motor, and rotating the screw after the screw tightening operation using the first voltage. The tightening torque is set by measuring the tightening torque with a torque wrench and repeatedly making adjustments so that the measured value reaches the desired tightening torque.

The drive circuit 5 is connected to supply a voltage for driving a DC motor 6, and a driver bit 7 is connected to the DC motor 6. Furthermore, a current detection circuit 8 is connected to the DC motor 6 to detect the load current as a voltage. This current detection circuit 8 is connected to a comparison circuit 9 and further connected to the switching circuit 1. A reference voltage setting circuit 10 is connected to this comparison circuit 9, and when the detected value of the current detection circuit 8, that is, the voltage corresponding to the load current reaches the reference voltage set in the reference voltage setting circuit 10, The switching circuit 1 is configured to be activated by a coincidence signal.
This reference voltage is set to a maximum voltage corresponding to the maximum load current flowing through the DC motor 6 when the first voltage is supplied to the DC motor 6. The voltage increases to a value close to the maximum load current, and the voltage is selected when the rotation of the DC motor 6 has sufficiently decreased. That is, the reference voltage is used to detect the point immediately before the screw tightening is completed;
The structure is such that the first voltage and the final voltage can be switched immediately before the screw tightening is completed. Further, this load current is not proportional to the actual tightening torque when the first voltage is supplied, but is proportional to the actual tightening torque when the final voltage is supplied.

Next, the operation of the present invention will be explained. A screw tightening start signal for starting this operation is applied to the switching circuit 1, and the first voltage is amplified by the amplifier circuit 4 and applied to the drive circuit 5. A constant driving voltage is supplied to the DC motor 6 according to this voltage, and the DC motor 6
starts rotating with a rotational torque lower than the desired tightening torque. Therefore, the driver bit 7 also rotates at the same time, and the screw tightening operation of the object to be fastened is started.

When the screw is screwed into the object to be fastened, the load current of the DC motor 6 gradually increases. When the screw head seat starts to come into contact with the mating material, the load current increases rapidly. At this time, the actual tightening torque of the screw does not reach the desired tightening torque. As the load current increases, the rotational speed of the DC motor 6 and driver bit 7 decreases, and when the load current approaches the maximum, the rotational speed becomes almost zero. This load current is detected as a voltage by the current detection circuit 8. When this voltage becomes a voltage corresponding to a value close to the maximum load current set in the reference voltage setting circuit 10 and the saturation state of the DC motor 6 is detected, that is, the time point immediately before the completion of screw tightening, the comparator circuit 9 sends a signal to the switching circuit. 1, a match signal is sent to switch the first voltage to the final voltage. Therefore, this final voltage is gradually applied to the amplifier circuit 4.
The signal is amplified and applied to the drive circuit 5. A predetermined drive voltage is supplied to the DC motor 6 in accordance with this final voltage, and the DC motor 6 is rotated at a higher voltage than in the case of the first voltage. At this time, the DC motor 6 and the driver bit 7 start rotating from an almost stopped state, and since a load is applied to the driver bit 7, the driver bit 7 rotates slowly and almost no inertia torque is applied to the driver bit 7. , the tightening torque increases to the rotational torque specified by the drive voltage, and the screw tightening work is completed. When the screw tightening torque becomes equal to this rotational torque, the driver bit 7 stops rotating, but the drive voltage to the DC motor 6 is then cut off by appropriate means.

As explained above, the present invention sets the voltage supplied to the motor in two stages, and supplies the motor with a voltage lower than the voltage required to obtain the desired tightening torque until just before the screw tightening is completed, and immediately before the screw tightening is completed. The high voltage required to obtain the desired tightening torque is supplied to the motor from the time of completion of screw tightening, and since this high voltage is gradually supplied to the motor, there is no inertia force at all just before the completion of screw tightening. Not only does this not occur, the motor has stopped rotating even when the screws are tightened, so no inertia is generated at all.
This method has the advantage that the tightening torque determined by the voltage supplied to the motor can be reliably obtained, and extremely accurate torque control is possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the operation of the present invention. 1...Switching circuit, 2...First voltage setting circuit, 3
...Final voltage setting circuit, 4...Amplification circuit, 5...
Drive circuit, 6... DC motor, 7... Driver bit, 8... Current detection circuit, 9... Comparison circuit,
10... Reference voltage setting circuit, 11... Delay circuit.

Claims (1)

[Claims] 1. The voltage supplied to the DC motor 6 is set in two stages, and the first voltage is supplied to the DC motor 6 from the start of screw tightening until immediately before the completion of the screw tightening, and from immediately before the completion of the screw tightening to the completion of the screw tightening. A two-stage tightening torque control device is configured to supply the final voltage to the DC motor 6 up to a maximum of 100 degrees, and to detect the point immediately before the completion of screw tightening from the value of the load current flowing through the DC motor 6. A voltage supply section connected to the DC motor 6 is provided with a first voltage setting circuit 2 that supplies a first voltage lower than the desired tightening torque and a final voltage setting circuit 3 that supplies a final voltage that yields the desired tightening torque. A switching circuit 1 is provided for switching from the first voltage setting circuit 2 to the final voltage setting circuit 3 via a delay circuit 11 that gradually applies voltage, which is made up of a capacitor and a resistor, and also changes the load current flowing through the DC motor 6 to the voltage. A reference voltage setting circuit 10 is provided to set a voltage corresponding to a value close to the maximum load current of the DC motor 6 to which the first voltage is supplied as a reference voltage. 2. A two-step tightening torque control device for an electric screwdriver, characterized in that a comparison circuit 9 is provided for comparing the detected value with a reference voltage and operating the switching circuit 1 based on a matching signal.